1. Field of the Invention
The present invention relates to an optical module such as an optical amplifier or a transponder mounted in annular form and, more particularly, to a reel and method for mounting an optical fiber in annular form.
2. Description of the Related Art
For an optical module used in optical communication systems, such as an optical amplifier or an optical transponder, an optical fiber used in the module is mounted on an optical fiber reel in order to house the optical fiber in a space of a small volume, as described in Japanese Patent Laid-Open Publication No. 2001-213573, for example.
In an erbium (Er) doped fiber amplifier (EDFA), which is a kind of optical amplifier, an Er-doped optical fiber (EDF) is mounted on an optical fiber reel and disposed in the amplifier. The EDF has a length of several meters to several tens of meters and used for amplifying light in a wavelength band ranging from 1530 to 1565 nm (C-band) or in a wavelength band ranging from 1570 to 1605 nm (L-band).
FIGS. 8 and 9 are diagrams showing optical fiber reels. Referring FIG. 8, in an optical fiber reel 60, an optical fiber 62 is wound around an outer peripheral surface 64 of an annular frame 66. A flange 68a, 68b may be provided on the periphery of each or one of opposite ends of the annular frame 66, and the optical fiber 62 is wound up between the flanges 68a, 68b. Reels having the structure shown in FIG. 8 can be those that do not have any flange. Referring FIG. 9, in an optical fiber reel 70, an optical fiber 72 is housed in a form of an annular bundle in an annular container 74.
In some optical amplifiers, in order to realize good amplification characteristics and compensate for internal loss, a plurality of amplifying units is used. In such cases, since each of the amplifying units has an EDF, a plurality of EDFs corresponding to the plurality of amplifying units is mounted on one optical fiber reel.
FIGS. 10 and 11 are diagrams showing arrangements in which a plurality of EDFs is mounted on one optical fiber reel. FIG. 10 shows a sectional view of a reel having a structure of four winding-up-type (bobbin-type) reels, such as shown in FIG. 8, used for four amplifying units. FIG. 11 shows a sectional view of a reel having a structure of four container-housing-type reels, as shown in FIG. 9, used for four amplifying units.
As shown in FIG. 10, in the winding-up-type reel, partition flanges 2, 3, and 4 are provided to extend from an outer peripheral surface of the annular frame, between opposite ends of flanges 1. EDFs 5, 6, 7, and 8, which are respectively associated with the amplifying units, are wound up against the surface of the frame with some pressure around portions between the partition flanges 2, 3, and 4. If the reel is made of a metal, a thickness for each flange of 1 to 4 is 0.5 mm at least and width necessary for the wound-up portions between the flanges is 1.5 mm at least. The width of the reel is about 3 mm. Accordingly, the reel height corresponding to the four amplifying unit, which is also a width of the annular frame, is 8.5 mm at least. Such a height is disadvantageous for reducing a size of the optical amplifier.
On the other hand, in the case of the container-housing-type reel shown in FIG. 11, as each of the EDFs 5 to 8 is bundled and housed, there is no need to provide any partition in the container. However, mounting density of the EDFs 5 to 8 on the container-housing-type reel is lower than the winding-up-type reel and the sectional area of the container is increased. For example, since the mounting density is about 20% in ordinary cases, in order to house 100 EDFs having a diameter of 0.25 mm, a sectional area of 6×6 mm including the sectional area of a 0.5 mm container wall is required.